The objective was to determine the cause of progressive debilitation and death of rhesus monkeys housed at contractor's facilities in Perrine, Florida. Many monkeys manifested typical signs and pathological lesions consistent with polychlorinated biphenyl (PCB) intoxication. Tissues from affected animals were analyzed and found to contain toxic levels of PCB's. The source of the PCB appears to be concrete sealer used on the outside runs. The runs were resurfaced with a polyurethane base material and the program has subsided. The investigation has been terminated.